FRANKFURT, Germany  —  Demonstrators blocked the entrance to the U.S. Rhein-Main air base near Frankfurt on Saturday as nearly 20,000 people protested against a looming attack on Iraq.

About 2,000 demonstrators rallied in front of the main gate to the base, a key transit point for U.S. military traffic to Afghanistan and the Persian Gulf, listening to speeches and scrawling anti-war slogans on the road in colorful chalk.

More than 300 police officers kept the protesters away from the base. No incidents were reported.

Earlier Saturday, about 10,000 people marched for peace in the city of Cologne, the latest in a series of big demonstrations that underline public support for Chancellor Gerhard Schroeder's opposition to a possible U.S.-led war in Iraq.

Elsewhere, 5,000 people demonstrated in Mannheim and 2,000 took to the streets of Koblenz in support of peace.